Recently, due to the spread of personal computers and mobile terminals, communication of digital data (data communication) via Internet has come into general practice. One of digital data distributed in data communication is an motion image. Since the motion image has large quantity of data, it is encoded with static images and associated voices (frames) as units before it is sent, thus reducing the data amount of the motion image.
As a method of encoding motion image data like this, there has been the method of encoding image data in which image coded data is provided with a function of enhancing precision of the decoded image (scalability) with the progress of decoding of image coded data obtained by encoding image data in motion image data.
For the conventional method of encoding image data, however, there have been cases where for some code length of image coded data having a scalability function, this image coded data could not be decoded within a time period over which the one-frame image is played back.